1. Field of the Invention
The present invention relates to a glaucoma drain for facilitating the flow of aqueous humor through the trabeculo-descemetic membrane.
Glaucoma is a chronic, progressive and irreversible disease of having excessive intraocular pressure. When there is an obstacle to the evacuation of aqueous humor from the anterior chamber through a filter known as the trabeculum, the intraocular pressure increases and causes the progressive destruction of the nerve fibers. There are medical treatments whose efficacy proves to be insufficient in numerous cases in which solely surgery can enable the intraocular pressure to be reduced.
The purpose of surgical operation for the treatment of glaucoma is to create a mechanism for reducing the intraocular pressure. There are currently two main categories of drainage operation, penetrating and non-penetrating. The commonest surgery is penetrating surgery and is termed trabeculectomy. It consists in creating a fistula between the anterior chamber of the eye and a subconjunctival space. This operation requires, apart from opening the chamber, the formation of an aperture in the sclera using a scalpel, giving rise to complications which lead to a high number of failures.
2. Description of Related Art
The categories of non-penetrating surgical operations include viscanalostomy and deep sclerectomy, also termed ab externo trabeculectomy. Dr Robert Stegmman's viscanalostomy (J Cataract Refract Surg, vol. 25, 1999) comprises preparing a fornix based conjunctival flap and cutting a first parabolic flap of a third of the thickness of the sclera, and a second parabolic scleral flap of a depth of almost two thirds the thickness of the sclera which is later removed, de-roofing Schlemm's canal and injecting high viscosity non-crosslinked sodium hyaluronate into Schlemm's canal and subsequently under the outer flap after suturing. A scleral reservoir filled with sodium hyaluronate is thus formed under the outer flap. The physiological porosity of the juxtacanalicular trabecular meshwork and the descemetic membrane enable aqueous humor to be evacuated and the intraocular pressure to be reduced. However, the sodium hyaluronate is eliminated within five to six days and the reservoir rapidly fills up with fibrosis limiting the duration of effectiveness of the operation.
A development of this technique is presented in the PCT application WO 98/35640 which describes a pre-descemetic sclero-keratectomy implant of crosslinked hyaluronic acid having the form of a prism with a triangular base. This implant is supposed to occupy the surgically created space for a longer duration, but the volume of the implant reduces by half in four months and is totally resorbed subsequently.
According to another variant form of Dr Mermoud's deep sclerectomy, a glaucoma drain of cylindrical form is produced from lyophilized porcine collagen and is sutured in the deep scleral bed. The drain transports aqueous humor by capillarity. The superficial scleral flap does not close the posterior end of the cylindrical drain which is ill-adapted to the configuration of the scleral reservoir. The drain is resorbed in the month following the operation.
All these glaucoma implants and drains produced from crosslinked and non-crosslinked hyaluronic acid or from collagen are resorbable and thus do not constitute a truly long-lasting solution for draining aqueous humor from the anterior chamber so ensuring sustained reduction of the intraocular pressure. Moreover, these implants and drains of animal origin have a high manufacturing cost risk transmitting diseases, in particular viral diseases, and when they are of porcine origin or treated with porcine heparin, surgeons face refusal of patients on religious grounds.
The application WO 95/35078 describes a sclerectomy implant, with or without incision of the trabeculum, made from methylmethacrylate/vinylpyrrolidone copolymer with a high water content of the order of 40% It comprises an intra-scleral part adapted to be positioned against the trabeculum within an opening under the scleral flap and a sub-conjunctival part which emerges from the sclera and is lodged under the conjunctiva. The outer end of the implant pours aqueous humor under the conjunctiva and forms a bleb which is visible through the conjunctiva.